Cylindrical drum-type wood chippers for reducing logs, ranches, roots, and the like to wood chips are well known. In general, drum-type chippers comprise a rotating cylindrical drum having an exterior surface studded either with hammers or sharpened chipper knife blades depending upon the desired consistency of the finished chips. Sharpened chipper blades, for example, tend to produce neatly cut wood chips while hammers tend to pulverize, shred, and tear the wood into randomly shaped shards. In use, logs and branches are fed to the rotating drum where the moving hammers or knives reduce them into small pieces that can be transported easily or be used for pulp, mulch, or the like.
Examples of drum type wood chippers are found in U.S. Pat. Nos. 4,802,631 of Arasmith, 4,785,860 of Arasmith, 1,418,735 of Plaisted, and 3,801,027 of Kubitz. In most of these examples, logs to be processed are fed to the surface of the rotating drum by a feeder mechanism such as a conveyor or feed roll. The blades of the drum are configured to impact, cut, and chip the log into pieces of roughly the same size, whereupon the pieces are discharged from the machine through a discharge chute.
Disc chippers have been developed as an alternative to drum type chippers. These disc chippers employ a rotating knife or hammer bearing disc rather than a cylindrical drum to reduce wood to chips. A good example of a disc chipper is presented in U.S. Pat. No. 4,827,989 of Strong. Other examples are illustrated in U.S. Pat. Nos. 1,195,774 of Brown, 3,732,907 of Nystrom, and 4,736,781 of Morey et al. In addition, a unique and improved disc type chipper is disclosed and claimed in my own U.S. Pat. No. 5,469,901, of which the present application is a continuation-in-part. The disclosure of my said patent is hereby incorporated by reference in order to provide a good background for the particular improvements and disclosures of the present application.
In general, disc type chippers comprise a housing that carries a rapidly spinning metal disc having knives or hammers mounted on the surface of the disc. Wood to be processed is fed to the disc surface, usually at an angle, where the knives or hammers reduce the wood to chips and shards. The chips and shards, when cut, can either pass through gullets in the disc, can be discharged through a sizing grate, or can be transferred to the back side of the disc for additional processing.
Many disc-type chippers and drum-type chippers have moving surfaces that are studded with hammers or knives that protrude outwardly from the surface. In the case of disc-type chippers having hammers, these hammers usually comprise a rectangular block of metal that is secured with screws or weld joints to the surface of the disc so that the hammers protrude therefrom. Usually, the hammers are arranged along preselected radii of the disc so that they can pass through slots formed in metal anvils that are secured adjacent to the surface of the disc. The interactions of the hammers and anvils generates a scissor action that shreds and cuts the wood into small pieces and shards that can be subsequently processed or discharged from the machine. Typically, as disclosed in my U.S. Pat. No. 5,469,901, the anvil of a disc chipping machine is located at the base of an infeed spout so that wood, usually in the form of tree limbs, is presented directly to the hammer/anvil interface as it is fed into the machine. In this way, the wood that is introduced through the infeed spout is immediately shredded and torn by the scissor action of the interacting hammers and anvil.
In the past, hammers such as those just discussed have generally been rectangular and have been formed of a single piece of hardened steel and anvils have been formed from a hardened steel bar having square transverse slots or grooves through which the hammers pass cut in one edge thereof. While this has proved somewhat acceptable for shredding and cutting wood, it nevertheless is plagued with various problems and shortcomings. For example, in disc-type chippers, a relatively large clearance must be provided in the slots of the anvil so that the rectangular hammers, which are actually traveling in circles, can pass through the slots in the anvil without engaging the sides thereof. This problem is particularly acute at positions nearest the hub of the disc, where the arc through which the hammers travel is the tightest. An additional problem with prior art wood chippers and hogs has been that the anvils generally are made of a single solid piece of hardened steel that is securely fastened to the frame of the machine adjacent to the rotating disc thereof. Such monolithic anvil designs, which have been relatively simple to manufacture, are nevertheless plagued with their own problems. For example, occasionally a stone or piece of metal will inadvertently be fed into the machine. Such foreign items can cause teeth of the anvil to be broken off when they encounter the interface between a moving hammer and an anvil slot. Broken anvil teeth reduce the efficiency of the entire machine and require that the anvil be replaced. In addition, anvils in wood chippers and wood hogs tend to wear at different rates along their length as a function of the distance along the anvil from the hub of the chipper. Accordingly, in some instances, the entire anvil must be replaced when only a portion of it is worn beyond use. Obviously, this is expensive and wasteful.
It has also been known in the past to provide disc and/or drum chippers and hogs with chip sizing grates for insuring that wood chips and shards expelled from the machine are of a predetermined maximum size. Examples of such grates are illustrated in my own U.S. Pat. No. 5,469,901 and in other U.S. patents including U.S. Pat. Nos. 4,802,631 of Arasmith and 4,958,775 of Arasmith. U.S. Pat. No. 4,077,450 of Ackerman illustrates a rotating drum chipper having holes or gullets formed in the drum through which wood chips pass as they are cut. However, this does not function to size the chips themselves but only to direct them away from the cutters as the wood is processed. Many prior art chip sizing grates have been relatively primitive and have simply comprised metal plates adjacent the cutting surface of the machine with holes formed in the plates for passing chips and shards when they reach a certain small size. Therefore, they have generally been limited in their function and generally serve as simple sieves for sorting chips into various sizes.
The inner surfaces of chip sizing grates are subjected during use to extreme abuse because of the violent and often abrasive nature of the cutting and tearing of wood by the hammers or knives.
Further, in grates such as that shown in Arasmith ('775) wherein gullets in the grate are provided with cutting or tearing surfaces, wood shards are forcibly engaged by these surfaces and directed through the gullets in the grate, which deteriorates and wears out the cutters and the gullet openings and can break off the cutters. For these and other reasons, chip sizing grates generally are subject to frequent and expensive replacement and repair.
In the past, foramanous chip sizing grates such as those discussed above have generally been designed to follow the contour of the cutting surface (be it a disc or drum surface) and to be fixed at constant spacing therefrom. While this has proved somewhat acceptable for shredding and cutting wood and sizing the resulting chips, it nevertheless is plagued with various problems and shortcomings. Certain designs of wood shredding machines, for example, utilize hammers of different protruding heights to break down wood or other materials into a smaller finished product. As a result, the path of hammers having the smallest protrusion from the rotating surface is significantly further away from the inner surface of the chip sizing grate than the path of the taller hammers. This creates voids in which material can become lodged, ultimately clogging the machine. In addition, since the edges or end faces of the gullets in the grate act to help cut and process the wood as the hammers pass the gullets, the hammers that are further from the grate do not cooperate efficiently with the gullets in the grate, resulting in less efficient overall machine operation.
Another problem, particularly with disc-type wood hogs, is that broken down wooden material tends to be slung by centrifugal force toward the outside peripheral portion of the rotating disc. While hammers and cutters actually move faster in these regions, the power required to break down wood here is significantly greater. In many instances, it is more efficient for the wood to be retained in a region closer to the hub of the disc until it is broken down into finer chips and shards and then moved to the peripheral portion of the disc for further processing.
Finally, a general problem with all types of wood chippers and hogs has been various voids in the spaces between the hammers or cutters on a rotating surface and the inner surfaces of the housing or grate. These voids occur, as mentioned above, partially because of different size hammers on the rotating surface with the inner surface of the grate necessarily being spaced from the surface a distance to accommodate the larger hammers. Voids also occur between the individual hammers in a series of aligned hammers, whether the hammers be short hammers or tall hammers. The most efficient processing occurs when the occurrence of voids of all types is minimized. The prior art has heretofore failed to address this general problem.
It will thus be seen that there exists a continuing need for a wood pulverizing machine such as a chipper or hog having improved hammer and anvil configurations designed to enhance the efficiency and function of the machine. Such hammer and anvil configurations should assure minimum clearance between the walls of the anvil slots and the hammers passing through to maximize the scissor-like action that shreds wood into chips and shards within the machine. In addition, an improved anvil design should permit placement of the anvil adjacent a hammer-bearing disc in any one of a variety of orientations relative to the radius of the disc to improve efficiency. Further, the anvil should be assembled in replaceable segments so that broken teeth of an anvil can be replaced without replacing the entire anvil.
Improved chip sizing grates and grate components are also needed. Such grates should cooperate efficiently with the rotating cutting or shredding surfaces of the machine, should be highly resistant to wear, tear, and breakage, should help prevent wood shards from being slung to the peripheral portions of a rotating disc too soon, and should be easy and simple to overhaul when necessary. There is a general need for a wood chipper or shredder in which the occurrence of voids in regions where wood is processed is reduced to a minimum. It is to the provision of a wood pulverizing machine having such improved hammer and anvil configurations, improved grates and grate components, and minimized voids that the present invention is primarily directed.